Correcting magnetic arrangement for deflection yokes



2 Sheets-Sheet 1 5 ma VG m7 5 N E E BEE/$430 B. (l/455175 E. GOSTYN ETAL CORRECTING MAGNETIC ARRANGEMENT FOR DEFLECTION YOKES Oct. 6, 1964 Filed Feb.

Oct. 6, 1964 E. GOSTYN ETAL 3,152,292

CORRECTINGMAGNETIC ARRANGEMENTFOR DEFLECTION YOKEZS Filed Feb. 1, 1962 2 Sheets-Sheet 2 2a 20 26 1a 2a 20 62a 34 3a 38 m 56 34 64H m z F/6.5 24 68 AITO/PNE rs United States Patent 3,1523% CORRECTING MAGNETIC ARRANGEMENT FOR DEFLECTION YOKES Ernest Gostyn and Bernard B. Chasens, Longmeadow, Mass., assignors to General Instrument Corporation, Newark, N.J., a corporation of New Jersey Filed Feb. 1, 1962, Ser. No. 170,428 Claims. (Cl. 317-400) The present invention relates to means for modifying the deflection of an electron beam such as occurs in cathode ray tubes, and is especially designed for correctmg distortions in the display image formed by such a beam on the screen of a cathode ray tube.

It is common todeflect an electron beam in a cathode ray tube, thereby to cause it to scan the screen of that tube, by means of a system of electrically energized coils which produce varying magnetic fields active upon the electron beam. Those coils are generally mounted upon a yoke fitted around the neck of the tube at an appropriate point. If the area of the screen were to have a shape which is substantially spherical, and with its center of curvature at the point where the beam is deflected by the magnetic fields produced by the windings on the yoke, an undistorted image would be produced on the screen. However, the screen, particularly in television receiving sets, usually departs quite materially from such an optimum spherical shape, with consequent distortion of the image formed thereon. Today television display tubes, particularly of the wide angle type, utilize screens which represent complex blendings of surfaces of varying large radii, such means being generally characterizable as square corner flat screens. With screens of this type complex distortions of the pin cushion type exist-the edges of a display which should be rectangular are in fact concave.

In the past correction of the deflection of the electron beam to compensate for the particular shape of the screen has been accomplished by mounting simple bar magnets on the deflection yoke, those magnets producsimple bar magnets has provided an acceptable degree of correction. However, this simple approach has not provided acceptable correction of the display image when screens of a more modern and more complex shape have been employed. Attempts to correct the display image of these newer style screens by means of simple bar magnets have required the use of eight or more of such magnets disposed at appropriate positions on the deflection yoke, and even then pole pieces of more or less complex shape have had to be used in combination with the permanent magnets. The use of such a large number of correcting magnets presents obvious problems in adjustment, assembly and maintenance, and adds appreciably to cost. All of these factors are of considerable importance, particularly in the home television field, Where competition is strong and cost is a very significant factor.

We have discovered that exceptionally effective cornpensation for distortion of the display image on complex shaped screens such as square corner flat screens can be I accomplished simply and reliably by utilizing, for such correction, permanent magnets of simple but unconventional shape. By using only two such unconventionally shaped correcting magnets, preferably in combination with two other conventional bar magnets, pin cushion distortion of the display image is substantially eliminated,

and without any appreciable degree of spot distortion which would tend to deteriorate picture definition.

More specifically, when two such magnets are located at diametrically opposite sides of the axis of the electron beam, the permanent biasing magnetic field which they produce is so shaped as to compensate for the concavity of the edges of the display formed on the screen in directions corresponding to the location of the magnets and also to assist in correcting for the concavity of the other edges of the display, particularly adjacent the corners of the display, thus, in most commercial cases, enabling simple bar magnets to complete the correction of the concavity of those other edges and produce a substantially rectangular display. The correcting magnets are disposed with one dimension (denominated their length) substantially perpendicular to the axis of the electron beam to be alfected, a second dimension of the magnets (either their width or thickness) being greater along an intermediate lengthwise portion thereof than at more outwardly disposed lengthwise portions thereof. In their preferred form the correcting magnets are of substantially uniform thickness, thus facilitating their mounting on the deflection yoke, are provided with a central lengthwise portion of given width, and are provided with endmost lengthwise portions of a lesser width. The transitions between the central lengthwise portion and the endmost lengthwise portions are substantially abrupt, and the magnets are disposed with their length.

substantially perpendicular to a line extending radially from the axis of the electron beam to be controlled, that line bisecting the length of the magnets.

The shape of these correcting magnets is such as to facilitate their manufacture and their assembly on the deflection yoke, thereby producing optimum correction of the display at minimal cost and with minimal trouble.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to an electron beam deflection assembly utilizing novel correcting magnets, as defined in the appended claims, and as described in this specification taken together with the accompanying drawings, in which:

FIG. 1 is a diagrammatic idealized view of a portion of a cathode ray tube display, illustrating certain corrections required to bring the display to the desired rectangular shape;

FIG. 2 is a side elevational View of a preferred form of the correcting magnet of the present invention and showing the shape of the magnetic field produced thereby;

FIG. 3 is a three-quarter perspective view of the correcting magnet of FIG. 2; 7

FIG. 4 is a front elevational view of a deflection yoke with correcting magnetsmounted thereon;

FIG. 5 is a side elevational view of the deflection yoke of FIG. 4; I

FIG. 6 is a fragmentary plan view, on an enlarged scale, of the magnet-mounting portion of the deflection yoke; and

FIGS. 7 and 8 are cross-sectional views taken along the lines 7-7 and 88 respectively of FIG. 6.

FIG. 1 illustrates a typical form of pin cushion type distortion such as is encountered on the screen of a television tube, and particularly such a tube having a wide angle type screen which is of the square corner flat type. The side edges 2 of the display is quite markedly concave, and the top and bottom edges 4 and 6 thereof are also concave, although usually with a somewhat greater radius of curvature than the side edges 2. (For simplicity of illustration the edges 2, 4 and 6 are shown as arcs of a circle. In practice they are usually more complex, with varying radii of curvature.) The arrows 8 extending laterally from different points on the side edge 2 to the straight line 10, which represents the desired corrected contour of the side edge of the display area, are indicative of the directions and relative magnitudes of the magnetic forces required to correct the deflection of the electron beam in order to produce a display having a straight side edge rather than a concave side edge 2. The broken lines 12 are indicative of the contour of the magnetic lines of force required to produce graduated correcting forces corresponding to the arrows 8.

With regard to the concave upper and lower edges 4 and 6, some of the concavity thereof can be eliminated if those edges are, in effect, pulled down adjacent the corners M which they make with the side edge 2 of the display, as by means of a magnetic force represented by the arrow 16. The broken lines 18 represent the contour of the magnetic lines of force required to produce a deflecting force corresponding to the arrow 16.

Analysis of FIG. 1 reveals that the sides edges 2 of the display can be corrected for pin cushion distortion, and the outer portion of the top and bottom display edges 4 and 6 can be correspondingly corrected, if there is superimposed upon the dynamic deflection field produced by the appropriately electrically energized deflection windings a fixed flux pattern possessing maximum corrective force at the location of the arrow 8a, progressively less corrective force as one moves toward the corners l4, and a force essentially at right angles to the other forces at the corners 14.

A composite flux pattern of the type required, and as indicated by the broken lines 12 and 18 in FIG. 1, is obtained by utilizing a corrective magnet 20 formed of appropriate permanent homogeneous magnetic material. These corrective magnets 2d are so shaped as to have a first dimension indicated by the arrow 22 which may be denominated their length, and a second dimension indicated by the arrow 24 which is perpendicular to the dimension 22 and which may be either width or thickness, although it is here specifically disclosed as constituting the width of the magnet 2d. The lengthwise central portion of the magnet 2d, generally designated 26, has a greater second dimension or width 24 than the endmost portions thereof, generally designated 28. Thus the correcting magnet 24) of FIGS. 2 and 3 has a long front surface 29, short end surfaces 32, abbreviated rear surfaces 34 near the ends thereof, additional end surfaces 36 and a central rear surface 33, the magnets 2% being of uniform thickness as disclosed, the shape of the magnet 20 in plan being characterizable as of the dual rectangle type, one rectangle being defined by the surfaces 36 and 38. A magnet of this configuration and formed as disclosed of permanent homogeneous magnetic material produces a magnetic field represented by the broken lines shown in FIG. 2. A comparison of the lines 12 and 18' of FIG. 2 with the lines 12 and 18 of FIG. 1 reveals that the magnetic field produced by the magnet 2% very closely approximates that required to produce the desired pin cushion distortion corrections illustrated in FIG. 1.

The manner in which the correcting magnets are used to correct a television tube display is illustrated in FIGS. 4-8 in conjunction with an otherwise essentially conventional deflection yoke generally designated 42. This yoke may comprise a pair of insulating frame pieces $4 on which two sets of deflection windings :6 and 48 are mounted, an appropriately shaped soft iron core 51 surrounding those windings and being held in place by a clamp 52,. The windings 46 and 48 produce magnetic fields disposed at right angles to one another, one field controlling horizontal deflection and the other controlling vertical deflection of the electron beam. The deflection yoke 42 is adapted to be received around the neck of a television display tube or the like, an axis of which is designated 54, the electron beam in that tube being adapted to move substantially along the axis 54 and to be deflected by the magnetic fields produced by the windings 46 and 48, which windings form magnetic fields appropriately oriented relative to the axis 54.

The frame pieces 44 are provided, at points diametrically opposed to one another relative to the axis 54 and appropriately related to the magnetic fields formed by the windings 46 and 48, with a pair of channel structures generally designated 56, which are adapted to receive and mount the correction magnets 2d. The channel structures 56 comprise an inner wall 58, a bottom wall 60 and an outer wall 62, the latter being formed of end portions 62a separated from a central portion 6211, all three portions being provided with inwardly directed enlargements 64a and 64b respectively, on their inner surfaces. The portions 62a and 6212 are somewhat resilient, and when the magnet 20 is inserted between the walls 58 and 62 and rests upon the bottom wall 60 it will be frictionally held in position, as best shown in FIGS. 6, 7 and 8. Once the optimum position of the magnet 20 in a given installation has been determined, as by actual test, the magnets 26 are then adapted to be fixed in that optimum position in any appropriate manner, as by the use of cement. The optimum position of the magnets 20 will be one in which, generally speaking, their relatively wide central portions 26 will be diametrically opposite one another, with each of the magnets 20 being substantially symmetrical lengthwise about a line extending radially from the axis 54.

The magnets 26 can be used to correct any desired pair of opposite sides of the cathode ray tube display, and two pairs of such magnets 26 could be employed, one pair for correcting the sides 2 of that display and another pair for correcting the top 4 and bottom 6 of the display. In the case of a rectangular display of the type shown in MG. 1, only one pair of magnets 20 need be employed, that pair of magnets 20 being located so as to modify the side edges 2 of the display, as indicated. When this is done, as has been explained, the end portions of the top and bottom edges 4 and 6 of the display adjacent the corners 14 thereof are also partially corrected for distortion, and adequate correction of the complete top and bottom display edges 4 and 6 can be accomplished by utilizing conventional correcting bar magnets 65 mounted in any appropriate manner on the frame pieces 44 at points in quadrature relation to the points where the magnets 25B are mounted.

As a result of the use of the magnets 20, eminently satisfactory pin cushion distortion correction is achieved, even when square corner flat screens are involved, through the use of but four correcting magnets, only two of which need be of the relatively complex configuration of the magnets 29. No special pole pieces are required, spot shape or focussing is not adversely affected, the individual correcting magnets may be easily manufactured, assembled and positioned, the overall cost of the resultant deflection assembly is minimized, and the correcting effect is reliable and not subject to dislocation.

While but a limited number of embodiments of the present invention have been here disclosed, it will be apparent that many variations may be made therein, all within the scope of the instant invention, as defined in the following claims.

We claim:

1. In an electron beam deflection assembly comprising a support, deflection coils fixed relative thereto and adapted to form a magnetic field relative to an axis, and a correcting magnet positioned relative thereto; the improvement which comprises said correcting magnet having a first dimension disposed substantially perpendicular to and laterally spaced from said axis, and having a second dimension substantially perpendicular to said first dimension and to said axis, said second dimension being greater at a portion of said magnet intermediate of said first dimension than along portions thereof more outwardly disposed along said first dimension and the transitions between said intermediate portion and said more outwardly disposed portions being substantially abrupt.

2. The combination of claim 1, in which said second dimension extends substantially radially outwardly from said axis.

3. The combination of claim 2, in which said intermediate portion of said magnet is disposed at a point substantially opposite the midpoint of the cross-section of the magnetic field produced by said deflection coils.

4. The combination of claim 1, in which said intermediate portion of said magnet is disposed at a point substantially opposite the midpoint of the cross-section of the magnetic field produced by said deflection coils.

5. The combination of claim 1, in which said magnet is mounted on said support with its second dimension extending substantially radially out from said axis, its surface closest to said axis extending in the direction of said first dimension and being substantially straight, said more outwardly disposed portions of said magnet having a given second dimension and the intermediate portion thereof having a greater second dimension, said magnet being substantially symmetrical about a line extending radially from said axis and said surface closest to said axis being substantially perpendicular to said line.

6. In an electron beam deflection assembly comprising a support, deflection coils fixed relative thereto and adapted to form a magnetic field relative to an axis, and a correcting magnet positioned relative thereto; the improvement which comprises said correcting magnet having its length disposed substantially perpendicular to and laterally spaced from said axis, and having a second dimension substantially perpendicular to said length and to said axis, said second dimension of said magnet being greater along an intermediate portion thereof than along the endmost portions thereof, the transitions between said intermediate portion and said endmost portions being substantially abrupt.

7. The combination of claim 6, in which said second dimension extends substantially radially outwardly from said axis.

8. The combination of claim 7, in which said intermediate lengthwise portion of said magnet is disposed at a point substantially opposite the midpoint of the cross-section of the magnetic field produced by said deflection coils.

9. The combination of claim 6, in which said intermediate lengthwise portion of said magnet is disposed at a point substantially opposite the midpoint of the cross-section of the magnetic field produced by said defiection coils.

10. The combination of claim 6, in which said magnet is mounted on said support with its second dimension extending substantially radially out from said axis and comprising the width of said magnet, its surface closest to said axis extending lengthwise thereof and being substantially straight, the endmost lengthwise portions of said magnet having a given width and the intermediate lengthwise portion thereof having a greater width, said magnet being substantially symmetrical about a line extending radially from said axis and said surface closest to said axis being substantially perpendicular to said line.

References fitted in the tile of this patent UNITED STATES PATENTS 2,157,182 Malofif May 9, 1939 2,553,039 Gray May 15, 1951 2,854,598 Baermann Sept. 30, 1958 2,92l,2l3 Reiches Jan. 12, 1960 2,954,494 Rennick Sept. 27, 1960 3,035,198 Skoyles May 15, 1962 

1. IN AN ELECTRON BEAM DEFLECTION ASSEMBLY COMPRISING A SUPPORT, DEFLECTION COILS FIXED RELATIVE THERETO AND ADAPTED TO FORM A MAGNETIC FIELD RELATIVE TO AN AXIS, AND A CORRECTING MAGNET POSITIONED RELATIVE THERETO; THE IMPROVEMENT WHICH COMPRISES SAID CORRECTING MAGNET HAVING A FIRST DIMENSION DISPOSED SUBSTANTIALLY PERPENDICULAR TO AND LATERALLY SPACED FROM SAID AXIS, AND HAVING A SECOND DIMENSION SUBSTANTIALLY PERPENDICULAR TO SAID FIRST 